Uefi boot the following diagram and table describe

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UEFI Boot The following diagram and table describe the different stages of the UEFI boot sequence:
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Stage Process SEC (Security) Immediately after the system is powered on, the SEC sequence begins. 1. Power is supplied to the CPU. 2. The CPU switches from 16-bit Real Mode to 64-bit Protected Mode. 3. The CPU executes a specific set of instructions to prepare the system for PEI to run. PEI (Pre-EFI Initialization) PEI initializes the system and prepares for the DXE. 1. The CPU and chipset are verified and fully initialized. 2. System memory is initialized, verified, and allocated. 3. PEI modules are loaded to allocate system resources. 4. The DXE is initialized, and the system is prepared to transition to DXE. DXE (Driver Execution Environment) DXE initializes configured devices, mounts drives, and prepares to boot the OS. 1. Device drivers are loaded into memory. 2. Hardware devices are initialized simultaneously (e.g., video card, network card, USB controllers). 3. System drives are mounted and initialized. 4. The EFI boot manager is initialized. BDS (Boot Device Selection) The BDS stage runs the EFI boot manager, which identifies the system's boot configuration settings and decides how to boot the system. 1. If an EFI System Partition (ESP) exists, the following process occurs: a. On the ESP in the \EFI\Microsoft directory, the boot manager looks for and runs the bootmgfw.efi file. b. The bootmgfw.efi looks for the BCD store in the same directory, which contains a list of all
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Windows installations. c. If only one installation exists, UEFI automatically loads it. If multiple installations exist, a list of bootable operating systems is displayed. 2. If no ESP exists, the boot manager uses Legacy BIOS mode to complete the boot sequence: a. The MBR looks for and loads the bootmgr.exe program. b. The bootmgr.exe program looks for the BCD store in either the C:\ directory or the System Reserved partition. c. If only one installation exists, bootmgr.exe automatically loads the OS. If multiple installations exist, a list of bootable operating systems is displayed. At the beginning of the BDS stage, the UEFI interface is executed and the option to load the EFI Shell or enter the UEFI configuration is available. TSL (Transient System Load) During TSL stage, the operating system loader is located and booted. 1. The BCD store is used to identify the location of the operating system loader (for Windows, the default location is C:\Windows\system32\winload.efi). 2. The operating system loader winload.efi is started. 3. Winload.efi then loads the following elements: a. System registry b. Ntoskrnl.exe c. Essential device drivers RT (Run Time) After the operating system and devices are configured, the system waits for user logon. Following logon, the operating system is configured with user-specific settings.
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